Past climates: Why the rate of change matters

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Plants and animals are adapted to their environment. When climate changes slowly, they can migrate to follow the conditions that suit them. But when climate changes quickly, plant populations sometimes can’t migrate fast enough and can be damaged before they have time to spread. This also impacts on animal populations which rely on vegetation for food and shelter.

Unlike animals, plants, trees and other vegetation grow fixed in one place. Except in cases of human intervention, plant populations can only migrate across successive generations, as new populations grow in new locations. Seed dispersal can be airborne or seeds can be spread by animals and insects. Although seeds can travel far and wide, there are limits to the distance and speed of dispersal. Gradual changes in climate tend to allow new populations time to establish themselves. More rapid changes can damage the new plants before they have time to grow and reproduce.

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Animal and insect populations can migrate far more swiftly than vegetation can. Animals don’t have to wait for the next generation to grow up – they can simply walk, swim or fly to a new location. But animal populations rely on plants and trees to provide a suitable habitat. Many animals are capable of adapting to new conditions and new types of habitat, but damage to large areas of vegetation can put pressure on local animal populations, as many creatures compete to find enough food and shelter in a reduced space. Because of this dependency on vegetation, animals as well as plants can be vulnerable to climate change.

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Obstacles such as mountain ranges, large areas of water or, more recently, human infrastructure can hinder the migration of plant and animal species. This can affect seasonal migrations as well as long-term population movements. Many species travel long distances each year to follow favourable seasonal climate conditions, but fragmentation of habitats or barriers along migration routes can make it harder for migrating populations to reach their destination. Plants and animals migrating in response to long-term climate changes also need viable migration pathways. The more obstacles that are present, the more difficult it is for species to move to new areas if local climate conditions become unfavourable.

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Seasonal changes in temperature and rainfall cause some regions to switch from warm to freezing – or wet to dry – conditions over just a few months. Yet these changes don’t have large-scale impacts on ecosystems, because plants and animals are accustomed to the yearly variations and have evolved to cope with them. Some species temporarily migrate, while others hibernate until the following year. Even a few years of unusually hot or cold conditions won’t usually pose a problem for natural systems. Environmental changes tend to have significant impact on plants, animals and ecosystems only when the changes are sustained over many years or decades.

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Plants and animals are usually well suited to the climates they live in, so changes in their environment can require migration, adaptation or both. Gradual changes are usually easier to adapt to than abrupt shifts in conditions, although both can prompt adaptation. If a change in climate persists for long enough, new species can evolve. In one example, scientists think a number of brown bears may have become isolated in the Arctic. Over successive generations, the bears developed characteristics better suited to their icy environment, such as lighter fur, eventually becoming a new species – polar bears.

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Shifts in climate create both winners and losers, as diverse species respond differently to the changes. For example, the dinosaurs – which had dominated the Earth for nearly 200 million years – died out 65 million years ago in a ‘mass extinction’ which scientists think was caused by rapid climate change. But the ancestors of modern mammal species survived and eventually prospered. Because mammals were very small at the time, they needed less food to survive than the larger dinosaurs and tended to live in underground burrows where they could shelter from extremes of weather on the surface. Over time, mammals grew both in size and in number – today there are more than 5000 species.

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Surviving helicopter fires and snowmobile crashes is all in a day’s work for Minna Valiranta in her efforts to learn how the climate has changed over the past 100,000 years. ‘My work involves collecting and identifying plant remains from sediment cores to help reconstruct past environmental conditions.’ Collecting these sediment cores from the Arctic is tricky work but has revealed surprising information about the vegetation that existed during ice-free periods. ‘By looking at old sediment layers we’ve discovered that trees grew in northern Finland around 90,000 years ago. The traditional view had been that this area was covered by tundra or ice. Our research completely changed this view.’

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There are many institutions and organisations around the world researching climate science, how our climate is changing, and ways of responding. Here are just a few…

British Antarctic Survey (BAS)

Department for the Environment, Food and Rural Affairs (Defra)

Department of Energy and Climate Change (DECC)

Energy Saving Trust (EST)

Environmental Change Institute (ECI)

European Space Agency (ESA)

The Geological Society (GS)

Grantham Institute for Climate Change (GICC)

Intergovernmental Panel on Climate Change (IPCC)

Met Office (MO)

National Academy of Sciences (NAS)

National Aeronautics and Space Administration (NASA)

National Oceanic and Atmospheric Administration (NOAA)

National Oceanography Centre (NOC)

The Royal Society (RS)

Tyndall Centre for Climate Change Research (TCCCR)

UK Climate Impacts Programme (UKCIP)

United Nations Framework Convention on Climate Change (UNFCCC)

World Climate Research Programme (WCRP)

World Meteorological Organization (WMO)

Climate change

A change in the climate that can occur over various time and spatial scales, including globally. Climate change has occurred naturally throughout the Earth’s history, with numerous causes such as changes in the Earth’s orbit, fluctuations in ocean circulations and variations in the Sun’s activity.

Over recent decades, the majority of climate scientists have concluded that the current period of global climate change is real and that human activities are the main driver.

Climate

A summary of the weather in a particular region over a period of at least ten years, but more commonly defined over 20 - 30 years. The climate describes both the average weather conditions (for example temperature, rain, snow and wind) in a particular region as well as the extremes.

Adaptation

Changes made to cope better with the impacts of climate change. Adaptation can occur in natural ecosystems, such as species migrating to more suitable climates, or in human systems, such as changes to buildings and sea defences or ways of life.

Arctic

The area around the North Pole, contained within the Arctic Circle (a circle of latitude drawn around the northern part of the globe). The Arctic is mainly ocean covered in floating ice which shrinks and grows in response to the northern hemisphere’s summer and winter.